Recombinant DNA Technology
- Junessa Masaya
- Apr 16
- 4 min read
HSC Biology | Free Study Notes
In this lesson
what recombinant DNA technology is
what plasmids do
how restriction enzymes are used
how ligase works
how transgenic organisms are produced
What is recombinant DNA technology?
Recombinant DNA technology is a process in which DNA from one organism is combined with DNA from another organism.
What this means
A selected gene can be:
removed from one organism
inserted into another organism
copied and expressed in the new host
Why this matters
This allows scientists to:
produce useful proteins
create transgenic organisms
investigate gene function
A 2025 HSC marking guideline describes recombinant DNA technology as selected genes being cut and pasted from one organism into another.
Plasmids
A plasmid is a small circular piece of DNA, commonly found in bacteria.
What plasmids do
In recombinant DNA technology, plasmids are often used as vectors.
A vector is something that carries the gene of interest into a host cell.
Why plasmids are useful
Plasmids are useful because they:
are small and easy to work with
can be inserted into bacteria
can be copied when bacteria reproduce
A 2025 HSC marking guideline specifically identifies a bacterial plasmid (circular DNA) being opened and used to insert a gene.
Restriction enzymes
Restriction enzymes are enzymes that cut DNA at specific sequences.
What restriction enzymes do
In recombinant DNA technology, restriction enzymes are used to:
cut out the gene of interest from donor DNA
cut open the plasmid vector
Why this matters
Using the same restriction enzyme on both the donor DNA and the plasmid helps produce matching ends, which makes it easier for the gene to be inserted.
A 2025 HSC marking guideline explains that restriction enzymes are used to cut a gene from human DNA and to open a bacterial plasmid using the same restriction enzymes. A 2024 HSC multiple-choice question also identified the production of sticky ends on both bacterial and human DNA as a key reason the technology works.
Ligase
DNA ligase is the enzyme that joins DNA fragments together.
What ligase does
After the gene has been inserted into the plasmid, ligase:
seals the DNA
joins the inserted gene to the plasmid DNA
helps create recombinant DNA
Why ligase matters
Without ligase, the donor gene and plasmid would not be permanently joined into one DNA molecule.
A 2023 HSC question listed creation of recombinant DNA joined using DNA ligase as one of the core steps in gene cloning, and 2025 HSC marking guidance states that the inserted gene is attached using DNA ligase.
The basic process
At this level, students should know the broad sequence.
Step 1: identify the gene of interest
A useful gene is selected from donor DNA.
Step 2: cut the gene and the plasmid
Restriction enzymes are used to:
cut the gene out
cut open the plasmid
Step 3: join the DNA
DNA ligase joins the gene into the plasmid, producing recombinant DNA.
Step 4: insert the plasmid into a host
The recombinant plasmid is introduced into a host organism, usually bacteria.
Step 5: copy or express the gene
As the host reproduces or expresses the gene:
many copies can be made
the host may produce the desired protein
A 2023 HSC multiple-choice question lists the broad gene cloning sequence as: extraction and amplification of DNA to be cloned, choice of host organism and cloning vector, creation of recombinant DNA using ligase, introduction into the host, and selection of organisms containing recombinant DNA.
Transgenic organisms
A transgenic organism is an organism that contains a gene from another species.
How transgenic organisms are produced
If recombinant DNA is successfully inserted and expressed, the host organism becomes transgenic.
Examples from HSC materials
HSC marking guidance describes:
bacteria carrying a human insulin gene and producing insulin
GM mosquitoes produced by transferring the SERPINE 1 gene using recombinant DNA technology
Bt corn, where a gene from Bacillus thuringiensis is inserted so the plant produces a protein toxic to a pest
Why transgenic organisms matter
They can be used to:
produce medicines
improve crop resistance
increase agricultural yield
reduce disease spread in some cases
Agricultural and medical use
Medical use
Recombinant DNA technology can be used to produce useful human proteins.
Example
A 2020 HSC marking guideline explains that bacteria with a human insulin gene can produce insulin, which can then be used to treat diabetic patients.
Agricultural use
Recombinant DNA technology can also be used to create organisms with useful traits.
Examples
pest-resistant crops such as Bt corn
modified microbes with improved fermentation ability, as described in a Year 12 problem set on genetically modified yeast strains
Why this topic matters in Module 6
This topic is important because it shows how humans can deliberately manipulate DNA to create useful outcomes.
It links to:
biotechnology
gene cloning
transgenic organisms
medical and agricultural applications
That is why recombinant DNA technology appears repeatedly in HSC questions and marking guidance.
Worked example
Exam-style question
Explain the role of plasmids, restriction enzymes and ligase in recombinant DNA technology.
Worked answer
Plasmids act as vectors that carry the gene of interest into a host cell. Restriction enzymes are used to cut the gene out of donor DNA and to cut open the plasmid. DNA ligase then joins the gene into the plasmid, forming recombinant DNA.
Why this works
This answer:
identifies the role of each component
follows the process in order
uses the key terms accurately
Common mistakes
Saying plasmids cut DNA. Restriction enzymes cut DNA.
Saying ligase cuts DNA. Ligase joins DNA.
Forgetting that plasmids are used as vectors.
Mixing up recombinant DNA technology with whole-organism cloning.
Describing transgenic organisms without explaining that they contain DNA from another species.
Quick quiz
What is recombinant DNA technology?
What is a plasmid used for?
What do restriction enzymes do?
What does ligase do?
What is a transgenic organism?
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